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Has anyone done a 10x scope amplifier?

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MrAl:
Hello there,

Do you know if anyone has done a 10x amplifier for a scope with bandwidth around 100MHz?

Alternately, does anyone want to design one maybe a group project?

Mechatrommer:
sorry for the quick rough "Dave" CAD.. its just a matter of finding the right opamp...

David Hess:

--- Quote from: MrAl on December 04, 2022, 12:05:38 am ---Hello there,

Do you know if anyone has done a 10x amplifier for a scope with bandwidth around 100MHz?

Alternately, does anyone want to design one maybe a group project?
--- End quote ---

What is the input impedance?  Are you intended to use this between a probe and the oscilloscope input?

Oscilloscope amplifier stages are typically differential transconductance amplifiers after the high impedance buffer and singled ended to differential conversion, which is where the offset or position signal is added.

An external x10 amplifier for a typical oscilloscope will require the high impedance buffer and controlled input capacitance.  There are some fast operational amplifiers now with a low enough input bias current to do this, barely.  I might use an LTC6269 dual with each amplifier configured for a gain of 3.2 and cascaded to make 10 and drive the oscilloscope input directly.  If the oscilloscope input is 50 ohms and a double termination is used, then the gain needs to be doubled to 20 and a higher power amplifier added, which suggests using a LTC6268 as a high impedance buffer, followed by the current feedback amplifier of  your choice providing the gain and high output current capability.

Andreas:

--- Quote from: MrAl on December 04, 2022, 12:05:38 am ---Do you know if anyone has done a 10x amplifier for a scope with bandwidth around 100MHz?

--- End quote ---
Hello,

what is the use-case for that?

And why do you think you can do a amplifier better than that what is already in your scope.
i.e. Without increasing the noise by the same factor as the amplification?

Noise is mainly definded by bandwidth and input impedance.
So there is not much improvement possible without reducing one of these parameters.

And yes I have made a 10000 fold amplifier for a scope: but with only 10 Hz bandwidth.

with best regards

Andreas

Karel:
Sacrificing bandwidth for gain and lower noise is a valid reason for using a preamplifier.
If the application is for audio (up to 20KHz) then I would recommend to use a pc soundcard with
appropriate software instead of a real scope.

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